The present invention is directed to ultracentrifuge rotors and, more particularly, is directed to a mechanical overspeed protection device in the form of a breakaway base on an ultracentrifuge rotor.
Ultracentrifuge rotors are designed to withstand stresses within specified limits. The centrifuges into which the rotors are placed in many instances have a capability of imparting rotational speeds greater than the design limits of the rotor. Typically incorporated into centrifuge machines are electrical overspeed protection circuits that should cause the centrifuge to cease operation if a preset speed is exceeded; however, these devices are not infallible. Therefore, in certain cases, the speed-limiting device should be an intrinsic part of the rotor itself.
If a rotor should exceed its design speed, the G forces on the rotor in the primary stress areas may cause fracturing of the rotor and rapid dissipation of the kinetic energy of the rotor. This not only causes damage to the rotor and the centrifuge, but also presents a possibly hazardous condition to the users of the centrifuge. Typically, centrifuges are designed to contain any physical fracturing of the rotor. However, damage to the rotor and the centrifuge would be minimized if there are limits on the speed at which the rotor can operate.
The Stahl et al. U.S. Pat. No. 3,990,063 patent discloses a mechanical overspeed device for an ultracentrifuge rotor. Incorporated in this design is a hub member on which the rotor resides for connection to the drive spindle. The hub is connected to the rotor by use of bolts that extend through the hub member and into the body of the lower portion of the rotor. Slots are formed in the hub member to establish a stress area. The hub is connected by the bolts through apertures in the hub to the rotor. During high speed centrifugation, if the specified safe speed is exceeded, stress in the areas adjacent the slots will develop sufficiently to cause a fracture in the hub member. However, the bolts must be sheared in order to allow complete disengagement of the hub member. Further, the insertion of the bolts completely into the body of the rotor creates additional stress regions that may be the source of eventual fracturing in the rotor itself.
Another approach to a mechanical overspeed protection device is shown in the Wright U.S. Pat. No. 3,961,745 patent. This device utilizes a handle on top of the rotor which will rupture if the rotor exceeds a certain speed. The resulting imbalance to the rotor will cause the rotor to disengage from the drive shaft.
Another type of mechanical overspeed device is shown in the Stallman et al. U.S. Pat. No. 3,101,322 patent wherein a pin is designed to move radially outward in the event of an overspeed condition and engage electrical connector to stop the rotor. In the Pickels U.S. Pat. No. 2,666,572 patent a similar arrangement is shown having a different shaped pin which is designed to move radially outward and engage a stop switch in the event of a rotor overspeed.
The desire to have a mechanical overspeed protection device on an ultracentrifuge rotor, in addition to electrical overspeed protection circuits, becomes more pertinent with respect to very high speed ultracentrifuges which are operating in the range of 30,000 to 100,000 RPM. In many instances these rotors are capable of attaining kinetic energies exceeding one-half million foot-pounds. Therefore, it is desirable to have a mechanical overspeed protection device which will prevent a rotor from reaching a speed at which a possible hazardous condition could occur.